Batman: The Killing Joke might be the 1st R rated animated movie
 

The producer for the upcoming adaption of the Killing Joke, says that Warner Bros gave them the approval for an R rated animated movie. Though it doesn't necessarily mean it be R rated, but they can go that route if they want.
http://www.polygon.com/2015/10/10/94...ecure-r-rating

We already have a thread: http://forums.thetechnodrome.com/showthread.php?t=52717